Electrical, optical, and structural properties of reactive ion beam sputtered hydrogenated amorphous germanium (<i>a</i>-Ge:H) films

Abstract

Electrical, optical, and structural properties of hydrogenated amorphous germanium (a-Ge:H) films prepared by reactive ion beam sputtering of a high-purity crystalline germanium target under varying deposition conditions have been studied. A detailed description of the deposition setup, preparation procedures, and techniques of property measurement is given. The dependencies on beam voltage, H2:Ar flow ratio, and substrate temperature of the room-temperature dark conductivity, optical band gap, hydrogen content, and ellipsometric and IR data are reported and analyzed. The minimum conductivity (10−4 Ω−1 cm−1) a-Ge:H films have been obtained for H2:Ar flow ratio of 16:1, and beam voltage and substrate temperature of 1000 V and 250 °C, respectively. These films contain a hydrogen concentration of about 11 at. % and show an optical band gap near 1.04 eV. The IR spectra reveal absorption bands corresponding to both monohydride (Ge-H) and dihydride (GeH2) groups for all the samples deposited. The monohydride absorption band is, however, completely absent in the films deposited at 350 °C. X-ray diffraction and spectroscopic ellipsometry analyses show that the films deposited at 350 °C are polycrystalline.